The present invention relates generally to magnetic resonance (MR) imaging systems. More particularly, the present invention relates to an MR imaging system equipped to reduce image artifacts caused by magnet vibrations produced therein.
When an object of interest, such as human tissue, is subjected to a uniform magnetic field (polarizing field B0, along the z direction in a Cartesian coordinate system denoted as x, y, and z), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it at their characteristic Larmor frequency. If the object, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated or xe2x80x9ctippedxe2x80x9d at a certain tipping angle, into the x-y plane to produce a net traverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation field B1 is terminated, and this signal may be received and processed to form an MR image.
When utilizing these signals to produce MR images, linear magnetic field gradients (Gx, Gy, and Gz) are also employed. Typically, the object to be imaged is scanned by a sequence of measurement cycles in which these gradient waveforms vary according to the particular localization method being used. The resulting set of received nuclear magnetic resonance (NMR) signals, also referred to as MR signals, are digitized and processed to reconstruct the image using one of many well-known reconstruction algorithms.
Ideally, a uniform magnetic field (B0) and perfectly linear magnetic field gradients (Gx, Gy, and Gz) would be utilized to image the object of interest. In reality, however, perturbation to the magnetic field, such as eddy currents, gradient amplifier infidelity, gradient non-linearity, magnetic field inhomogeneity, and Maxwell terms, can exist, resulting in image artifacts such as blurring, distortion, ghosting, and shift in the reconstructed MR image. In recent years, as magnets included in MR imaging systems have become smaller in size and weight in order to reduce cost, another perturbation factor is emerging as an important source of image artifacts.
As magnet size and weight are reduced, magnet vibration is becoming an increasingly serious problem. Magnet vibration causes perturbation magnetic fields, i.e., magnetic fields with vibration components, to be applied to the object of interest. In turn, these vibration components produce undesirable image artifacts in the reconstructed MR image. Constrained by cost, it is often difficult to proactively design magnets to completely eliminate all critical vibration components.
Thus, there is a need for an MR imaging system capable of correcting or compensating for image artifacts caused by magnet vibration before reconstructing an MR image. In order to do so, there is a need for an MR imaging system capable of quantifying the magnetic field vibration components.
One embodiment of the invention relates to a method for reducing image artifacts caused by magnet vibration in an MR imaging system. The method includes quantifying a vibration error component included in a perturbation magnetic field. The perturbation magnetic field is compensated to acquire k-space data corresponding to an MR image.
Another embodiment of the invention relates to an MR imaging system for reducing image artifacts caused by magnet vibration. The system includes a system control. The system control is capable of configuring a compensating magnetic field to offset a perturbation magnetic field produced by magnet vibration. The system control is further capable of calculating a vibration error component included in the perturbation magnetic field.
Still another embodiment of the invention relates to an MR imaging system for reducing image artifacts caused by magnet vibration. The system includes means for configuring a pulse sequence to acquire k-space data corresponding to an MR image. The pulse sequence includes compensating magnetic fields. The system further includes means for calculating a vibration error component included in the pulse sequence. The means for configuring is coupled to the means for calculating.